U.S. Pat. No. 3,852,365 discloses the preparation of perchlorofluorobenzenes by heating a reaction mixture consisting essentially of two or more perhalobenzenes selected from the group consisting of hexachlorobenzene, hexafluorobenzene and perchlorofluorobenzenes in which the number of chlorine or fluorine atoms in the components of the mixture differ by at least two. The reaction is conducted in sealed gold tubes at 500.degree. C. for three hours under 500 to 1000 atmospheres of pressure. No catalyst is present other than the interior of the gold tube.
U.S. Pat. No. 3,231,625 discloses the disproportionation of tetrafluorodichlorobenzene and trifluorotrichlorobenzene. The reaction is conducted at temperatures above 600.degree. C. in the presence of an aluminum fluoride catalyst. Below 600.degree. C. little or no disproportionation occurs.